The present invention relates to a navigation system for inducing and guiding a route from a starting point to an object point, and more particularly, a vehicle position detecting apparatus for precisely obtaining the present position of a moving body such as motorcar or the like running on roads.
In the conventional vehicle position detecting apparatus, the moving distance and the advancing direction of the vehicle are obtained respectively from a distance sensor and a bearing sensor. A method is devised of estimating a motorcar position and computing running loci using self-supporting navigation, while effecting correlation with respect to geography data stored in the memories of a CD-ROM and so on. The conventional vehicle position detecting apparatus is disclosed in, for example, Japanese Laid-Open Patent application Tokukaihei No. 2-130415. The construction of the conventional art is shown in a block diagram in FIG. 33.
A distance sensor 2601 outputs pulse signals for each unit running distance in accordance with the rotation of a tire. The running distance of the vehicle can be known by counting the number of the pulses. The direction sensor 2602 detects the turning angle speed (Yawrate) of the vehicle so as to output signals proportional to the turning rate of the vehicle. The output signals of both the sensors are inputted to a signal processing apparatus 2603 so that here the positions of the vehicle are obtained by the successive computation on the X-Y coordinates. The positional information computed for each unit distance running operation is stored in the running locus storing apparatus 2604. The road data are selectively read in the necessary portion only by the storing medium reproducing apparatus 2606 from what is stored in the map information storing medium 2605. The present positions computed by the signal processing apparatus 2603 are superposed on the surrounding road map and displayed on the display apparatus 2607. The operating apparatus 2608 controls a change in the scale ratio of a map to be displayed and a change in the display direction.
In accordance with the conventional embodiment, the running locus of a vehicle is approximated in broken line in the straight line of a constant distance. The estimated present positions of the vehicle are respectively set on the road during the running operation at present and all the roads to be branched from the road, with the road being also approximated in the broken line as in the locus line. Then, the locus and the road are superposed so that the deviation between the broken line vectors for constituting the locus and the broken line vector for constituting the road. The processing is effected on all the roads, the estimated present position on the road where the deviation of the vectors may become minimum is made the present position. When the roads are complicated in the processing, the number of the extracted roads increases. The distance between the present position deviated from the road and the estimated present position on the road is obtained. By a selection of one smaller than the given value, the estimated present position on the road which becomes a candidate of the present position is reduced so as to reduce the computation load.
There is also a method of effecting the positional calculation of the vehicle by the reception of electric waves from satellites. Generally a whole world positioning system (Global Positioning System, referred to as GPS) generally called an electric wave navigation is used. The electric waves from at least three satellites are received so as to obtain the distance to the satellite for effecting the positioning operation with three-sides location survey. Two methods are used alone or by combination. The present position together with the map information, around the vehicle position, obtained is a displayed on the display apparatus such as CRT or the like with the present position of the vehicle being computed.
In order to compute the position of the vehicle with high accuracy, it is necessary to stabilize the output of each sensor. There is a problem in that especially in the distance sensor, a difference is caused between the running distance to be obtained from the output of the distance sensor and the actual running distance due to aging factors such as the air pressure changes and so on of the tire. In order to solve these problems, a positioning position is considered to be used by GPS. For example, in Japanese Tokukaihei No. 1-142412, the distance conversion constant of the distance sensor output was considered to be corrected from the history of the positioning position by the GPS receiver.
In a vehicle position detecting apparatus of the conventional art, the road data of high accuracy is necessary. Much labor is needed to improve the accuracy of the road data. It is impossible to obtain the road data without errors so as to make new roads day by day. It is impossible to make the estimated present position in a correct position unless the roads are described in the road data when, for example, the newly opened road has been passed. Also, the curves are simplified due to data amount reduction, and the intersecting points also may become different in actual shape. The square computation is necessary to compute the distance, which requires a lot of time for the calculation. In the conventional art, the pattern matching between the road data and the locus are effected unconditionally so that the correct positional detection cannot be detected when errors exist in the shape of the road data as the reference. When the shape of the road data is different from the shape of the actual road, there is a problem in that the correct positional detection cannot be effected.
Also, when the GPS is used, especially when the positioning operation is effected with the use of GPS in cities, even when the value of the geometrical accuracy reduction ratio called GDOP in satellite arrangement is small, the positioning accuracy is often reduced due to the influences of the indirect waves reflected by the interference such as buildings of the road surrounding portion, the accumulation of the errors cannot be neglected when the actual running distance has been obtained by the integration of the distance between GPS positioning positions, with a problem that the calibration accuracy of the distance conversion constants of the distance sensor output is lowered.
In a vehicle position detecting apparatus of the conventional art, the user has to correct the road data. The correction of complicated portions which have many intersecting points requires a lot of labor. The road data to be used for the map match processing for obtaining the present position on the road through the comparison between the running locus of the vehicle and the road shape have more information as compared with the road data for display use of the information and so on about the connection of the road so as to require a large amount of labor, with a problem that the correct positional detection cannot be effected unless the user has to effect the proper correction.